New Ring and Pinion Gear Set Break-In

Breaking-In a new Ring and Pinion Gearset?

Frequently we hear people say; “Do I really need to break-in a new ring and pinion? I have never heard of having to do that before!” We also hear; “When I bought my truck new, I was never told about having to break-in the rear axle.” I can understand the reason behind this question and will explain it in more detail.

When you purchase a new vehicle from the dealership, we are told to drive easy for the first few hundred miles. This is to allow the engine to break-in properly. This makes sure the rings, valves and bearings are given time to wear-in properly and get established before being put under a load. What people do not realize is when you are breaking-in the engine, you are doing the same for the axle assembly.

Why do I have to break-in a ring and pinion gearset?

When your vehicle is being used without any modifications including stock tires, break-in is not as critical because the vehicle is being driven around town and being put under a load. People do not realize oversized tires put an unusual load on axles so make sure to follow the correct procedures. The result of improper break-in is ring and pinion burn. Vehicles more susceptible to gear set burn are wreckers, cab and chassis work truck trucks. Also vehicles tall gear ratios and vehicles with oversized tires. These types of vehicles can generate a lot of heat in the axle and cause the oil to fail. Following a proper break-in period includes cooling off periods so this will not happen. If you have a wrecker or a work truck, you can not pull a load until the break-in is done. If the gears are burned up, the warranty will be voided.

How does break-in help the ring and pinion gearset last longer?

When the manufacturer designs ring and pinion sets, the new gears are tapered during the building process. Gears are tapered to help keep humming noises down and it also keeps them cool during operation. However, when they are lapped during the build process, the pressure used is much less than what driving creates. During the break-in period, there are very small high spots on the gear teeth that get pushed back into the metal. This is called “work hardening”.  Work hardening happens when the metal surfaces are lubricated properly and kept cool. If the temperature gets too high, the metal will soften and the gears will start to break down. So…keep the axle cool and not under an excessive load during break-in. That way you will set and enjoy years of operation with normal use and proper maintenance.

How do I break-in a new ring and pinion gearset in a rebuilt axle/differential?

Most of our rebuilt axle assemblies come already filled with fluid. When following the proper break-in schedule, the oil needs to be changed at 500 miles. This cleans out the debris and phosphorous coating caused by break-in and will protect the axle from premature failure. Even if you prefer synthetic oils, break-in must still be followed.

Break-in Technique:

After the axle is installed, run it in the air for about 15 minutes then let it cool before starting your road break-in. Afterwards, drive the first 15-20 miles, stop the vehicle and allow the axle to cool. Make sure to keep speeds under 60 miles per hour for the first 100 miles. Then for the next 500 miles, do not tow a vehicle or put the gear set under a heavy load. When you do use the truck for heavy work or towing, stop after 15 miles of driving to allow an additional cooling period. This is needed because not all of the teeth are fully meshed together until fully loaded.

It is very easy to damage the teeth under a load if break-in is not followed and will void the warranty. If you have a limited slip differential installed, too much additive can lead to failure. Use enough to stop the clutches from chattering but not more than 4 ounces for every 2 quarts used to fill the axle.

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